Antifouling structure precursor, antifouling structure, surface modification composition and surface modification method

ABSTRACT

A surface modification method for modifying a surface of an oxide includes: producing a surface modification composition; and applying the surface modification composition onto the surface of an oxide layer. In producing the surface modification composition, a modifier having a perfluoropolyether chain is mixed with a first modification accelerator containing an inorganic acid and a second modification accelerator containing at least one selected from the group consisting of a metal, a metal salt and an organometallic compound.

TECHNICAL FIELD

The present invention relates to an antifouling structure precursor, anantifouling structure, a surface modification composition and a surfacemodification method. In more detail, the present invention relates to anantifouling structure precursor and an antifouling structure that can beproduced by a simple process and to a surface modification compositionfor producing the antifouling structure precursor and a surfacemodification method.

BACKGROUND ART

It has been known to treat the surface of a base material such as glassor plastic with a surface treatment agent to impart water repellency,oil repellency and antifouling property.

For example, Patent Document 1 discloses that a surface treatment agentthat contains a silane compound having a specific perfluoro (poly) ethergroup can form a layer that has high surface slipperiness and highabrasion resistance as well as water repellency, oil repellency,antifouling property and waterproofing property.

CITATION LIST Patent Document

Patent Document 1: JP 5835512 B

SUMMARY OF INVENTION Technical Problem

However, the surface modification of Patent Document 1 is achieved byvapor deposition, which is not a simple process and requires largeequipment.

The present invention has been made in view of the problem in the priorart, and an object thereof is to provide a surface modification methodthat enables forming an antifouling structure on a base material withlow heat resistance, such as resin, by a simple process.

Solution to Problem

As a result of a keen study for achieving the above-described object,the present inventors have found that an antifouling structure precursorcan be produced in an environment at ordinary temperature and ordinarypressure in a short time by modifying the surface of an oxide layer witha surface modification composition that concurrently contains amodification accelerator for accelerating hydrolysis and a modificationaccelerator for accelerating dehydration condensation. The presentinvention has been thus completed.

That is, the surface modification method of the present inventioninvolves producing a surface modification composition and applying thesurface modification composition to the surface of an oxide layer.

In producing the surface modification composition, a modifier having aperfluoropolyether chain is mixed with a first modification acceleratorcontaining an inorganic acid, and a second modification acceleratorcontaining at least one selected from the group consisting of a metal, ametal salt, and an organometallic compound.

The surface modification composition of the present inventionconcurrently contains: a modifier having a perfluoropolyether chain; and

a first modification accelerator containing an inorganic acid; and asecond modification accelerator containing at least one selected fromthe group consisting of a metal, a metal salt and an organometalliccompound.

A surface modification composition set of the present invention is acombination of the above-descried modifier, the above-described firstmodification accelerator and the above-described second modificationaccelerator.

The antifouling structure precursor of the present invention includes:an oxide layer; and a modification layer containing a modifier having aperfluoropolyether chain that covers an entire surface of the oxidelayer.

The modification layer has an uneven film thickness, and a coverage rateof covering the oxide layer with a comparatively thick area is equal toor greater than 10%.

The antifouling structure of the present invention includes theabove-described antifouling structure precursor that is impregnated witha lubricant oil.

Advantageous Effects of Invention

In the present invention, the surface of the oxide layer is modifiedwith the surface modification composition that concurrently contains themodification accelerator for accelerating hydrolysis and themodification accelerator for accelerating dehydration condensation.Therefore, it is possible to provide the surface modification methodthat enables producing the antifouling structure precursor at ordinarytemperature and ordinary pressure in a short time.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of an example of theantifouling structure precursor of the present invention.

FIG. 2 is a schematic cross-sectional view of an example of theantifouling structure of the present invention.

FIG. 3 is AFM phase images of examples and a comparative example.

DESCRIPTION OF EMBODIMENTS

Surface Modification Composition

The surface modification composition of the present inventionconcurrently contains a modifier, a first modification accelerator and asecond modification accelerator. It may further contain water, ifnecessary.

The modifier contains a compound having a perfluoropolyether chain.

Examples of such modifiers include silane coupling agents known in theart that have a hydrolysable group capable of binding to an oxide suchas alkoxy group or ester group.

The first modification accelerator contains a hydrolysis catalyst thatmainly accelerates hydrolysis of the modifier.

Such hydrolysis catalysts include inorganic acids, and such inorganicacids include phosphoric acid, diphosphoric acid, polyphosphoric acid,sulfuric acid, sulfurous acid, hydrochloric acid, nitric acid, boricacid and the like.

The second modification accelerator contains a dehydration condensationcatalyst that mainly accelerates dehydration condensation of themodifier. Such dehydration condensation catalysts include metalcatalysts, metal salts, organometallic compounds and the like.

Specific examples of such catalysts include metal catalysts such asplatinum and rhodium, metal carboxylates such as zinc octoate, tinoctoate, cobalt octoate and tin oleate, dibutyltin dilaurate, dibutyltindioctoate, dibutyltin diacetate, and hydrosilylation catalysts such asPt/1,3-divinyltetramethyldisiloxane complex and hexachloroplatinic (IV)acid.

The first modification accelerator and the second modificationaccelerator may be added in a so-called catalytic amount. For example,depending on the type of modifier used, the concentration of the firstmodification accelerator or the second modification accelerator in thesurface modification composition is within the range of 1.0 ppm to 20%.

The modifier produces silanol (Si—OH) as a result of hydrolysis, and thesilanol causes dehydration condensation to form a siloxane bond topolymerize the modifier itself while the silanol also causes dehydrationcondensation with a hydroxyl group on the surface of an oxide so as tomodify the surface of the oxide.

The surface modification composition concurrently contains the firstmodification accelerator and the second modification accelerator, andthey do not act as a catalytic poison of each other while acceleratingthe hydrolysis reaction and the dehydration catalytic reaction of themodifier. Therefore, it is possible to modify the surface of an oxide atordinary temperature in a short time only by applying the compositionand drying it.

Further, the surface modification composition can impart goodantifouling property even to the surface of an oxide layer that isformed on a base material with low heat resistance such as resin.

A modification layer formed by the surface modification composition hasuneven film thickness. That is, it forms a comparatively thick area anda comparatively thin area.

It has not been revealed yet why the surface modification compositionforms such an uneven modification layer. However, it is suggested asfollows.

Since the surface modification composition concurrently contains thefirst modification accelerator that accelerates hydrolysis of themodifier and the second modification accelerator that acceleratesdehydration condensation of the modifier, the modifier is polymerized bythe hydrolysis reaction to have wider molecular weight distributionbefore applying the surface modification composition onto the oxidelayer.

Then, the application onto the oxide layer causes dehydrationcondensation reaction, and the surface of the oxide layer is coated byvarious sizes of the modifier with different molecular weights. As aresult, the high-molecular-weight modifier forms the thick area whilethe low-molecular-weight modifier forms the thin area.

When the surface modification composition contains water, it can promotethe hydrolysis reaction to polymerize the modifier in a short time.However, hydrolysis of the modifier is also caused by water in the air.

The amount of water added in the surface modification composition ispreferably less than ten times the weight of modifier. When water isadded in the amount of ten times or more of the weight of the modifier,it inhibits the dehydration condensation reaction, and the surface ofthe oxide cannot be sufficiently covered.

Surface Modification Composition Set

Since the surface modification composition contains the firstmodification accelerator that promotes hydrolysis of the modifier tocause polymerization, the modifier sometime precipitates when thesurface modification composition is stored for a long time.

However, the composition can be stored for a long time as the surfacemodification composition set in which the modifier, the firstmodification accelerator and the second modification accelerator arestored individually in separate containers.

Surface Modification Method

The above-described surface treatment method, which modifies the surfaceof the oxide layer to decrease the surface free energy of the oxidelayer so as to improve the affinity for lubricant oil, involvesproducing a surface modification composition and applying the surfacemodification composition.

In producing the surface modification composition, the surfacemodification composition is produced from the surface modificationcomposition set, i.e. the modifier is mixed with the first modificationaccelerator and the second modification accelerator. When mixing themodifier, the first modification accelerator and the second modificationaccelerator, water may be further mixed at the same time in order topromote the hydrolysis reaction.

Alternatively, the surface modification composition may be produced andstored in a sealed container so that hydrolysis is not caused by waterin the air, and water may be added before use. Adding water afterproducing the surface modification composition and before applying thesurface modification composition onto the surface of the oxide layer canprevent development of the hydrolysis reaction.

In applying the surface modification composition, the surfacemodification composition is applied onto the surface of the oxide layer.

A coating method known in the art may be employed. Examples of suchmethods include, for example, spin coating, spraying, roll coating, flowcoating, dip coating and the like.

The surface modification composition is applied onto the surface of theoxide layer preferably after the elapse of preferably 15 minutes ormore, more preferably 2 hours or more from the production of the surfacemodification composition. Just after the production of the surfacemodification composition, the modifier has not been sufficientlypolymerized yet. Since the thick area is not sufficiently formed, thesurface free energy of the antifouling structure precursor may notsometimes be decreased.

The modifier may sometimes precipitate when the surface modificationcomposition is stored for a long period of time, e.g. several months ormore after the production. To avoid this, it is preferred that thesurface modification composition is applied within 1 month from theproduction.

The surface modification composition of the present invention thatconcurrently contain the first modification accelerator and the secondmodification accelerator can modify the surface of the oxide layer at anordinary temperature of, for example, from 20° C. to 30° C. In terms ofaccelerating the hydrolysis, it is preferred that the modification layeris formed in an environment at a humidity of 40% RH or more.

Antifouling Structure Precursor

The antifouling structure precursor of the present invention will bedescribed in detail. The antifouling structure precursor includes themodification layer that has low surface free energy and high affinityfor lubricant oil. The antifouling structure precursor becomes theantifouling structure by being impregnated with lubricant oil to form asmooth water-repellent surface.

FIG. 1 is a schematic cross-sectional view of the antifouling structureprecursor of the present invention.

As illustrated in FIG. 1, the antifouling structure precursor 1 includesthe oxide layer 2 and the modification layer 3 that contains themodifier having a perfluoropolyether chain. The entire surface of theoxide layer 2 is covered with the modification layer 3. Since the entiresurface of the oxide layer 2 is covered with the modification layer 3,the entire surface of the antifouling structure precursor 1 is wet withlubricant oil. Therefore, dirt is not pinned but slides off.

The modification layer 3 includes the comparatively thick area 31 andthe comparatively thin area 32. The comparatively thin area is dispersedin the comparatively thick area, and the coverage rate of covering theoxide layer with the comparatively thick area 31 is equal to or greaterthan 10%.

When the coverage rate of covering the oxide layer with thecomparatively thick area 31 is equal to or greater than 10%, theantifouling structure precursor has sufficiently decreased surface freeenergy and exhibits stable antifouling performance.

It is preferred that the coverage rate of covering the oxide layer withthe thick area 31 is within the range of 10% to 99%, more preferablyfrom 20% to 90%, yet more preferably 50% to 90%.

When the coverage rate is within the above-described range while theoxide layer 2 has a smooth surface, the modification layer with unevenfilm thickness forms an uneven pattern on the surface of the antifoulingstructure precursor. Since lubricant oil is likely to be held inrecesses, this improves the retention in combination with the highaffinity of the modification layer for lubricant oil.

When the oxide layer 2 has an uneven surface, the low-molecular-weightmodifier is likely to penetrate into recesses of the oxide layer 2 whilethe high-molecular-weight modifier modifies protrusions of the oxidelayer 2. As a result, a larger uneven pattern is formed on the surfaceof the antifouling structure precursor. This further improves theretention of lubricant oil.

The coverage rate of covering the oxide layer with the thick area can bemeasured with an atomic force microscope (AFM) by obtaining a shapeimage (uneven pattern image) of the surface of the antifouling structureprecursor along with a signal representing the physical property of thesurface at the same time and mapping the thick area based on an analyzedphase image.

Since the modification layer has different cohesive forces between thethick area and the thin area, the phase difference between vibration (ACvoltage) applied to an AFM probe and the vibration of a cantileverchanges. The film thickness of the modification layer can be evaluatedby mapping the phase difference, and the coverage rate of covering theoxide layer with the thick area can thus be measured.

The oxide layer is made of an inorganic oxide and has a hydroxyl groupin the surface. Examples of such layers include inorganic glass coatingformed on a resin-coated surface, glass, metal oxides and the like.

Such inorganic glass coating can be formed by applying a solution ofpolysilazane such as perhydropolysilazane (PHPS) onto a resin-coatedsurface and drying it.

It is preferred that the oxide layer has an uneven surface. When theoxide layer has an uneven surface, a larger uneven pattern is formed onthe surface of the antifouling structure precursor. This can improve theretention of lubricant oil.

The antifouling structure precursor can be formed by applying thesurface modification composition of the present invention onto thesurface of the oxide layer and drying it.

Antifouling Structure

As illustrated in FIG. 2, the antifouling structure 10 of the presentinvention includes the antifouling structure precursor 1 that isimpregnated with lubricant oil 4.

The lubricant oil 4 forms the smooth surface of the antifoulingstructure precursor 1 to repel foreign matters such as water, oil, sandand dust so as to reduce adhesion of such foreign matters.

Lubricant oils that can be used include non-volatile lubricant oilshaving low surface energy such as fluorinated oils and silicone oils.

Such fluorinated oils include fluoropolyether oils, perfluoropolyetheroils and the like.

Such silicone oils include straight-chain or cyclic silicone oils.

Examples of straight-chain silicone oils include so-called straightsilicone oils and modified silicone oils. Examples of straight siliconeoils include dimethyl silicone oil, methylphenyl silicone oil,methylhydrogen silicone oil and the like.

Examples of modified silicone oils include straight silicone oils thatare modified with polyethers, higher fatty acid esters, fluoroalkyls,amino, epoxy, carboxyl, alcohols.

Examples of cyclic silicone oils include cyclic dimethylsiloxane oil andthe like.

EXAMPLES

Hereinafter, the present invention will be described in detail withexamples.

However, the present invention is not limited to the following examples.

Comparative Example 1

Production of Surface Modification Composition

A surface modification composition was produced by mixing 10 mL of amodifier having a perfluoropolyether chain (FLUOROSURF FG-5020TH-0.1,Harves Co., Ltd.) with 2.5 μL of alkoxysilane containing 20% ofphosphoric acid as the first modification accelerator and 666 μL of anisopropyl alcohol solution containing 3 ppm of an organic platinumcatalyst (Pt/1,3-divinyltetramethyldisiloxane complex) as the secondmodification accelerator.

Production of Modification Layer

The surface modification composition was applied onto a smooth glasssurface by using a cotton, and the applied composition was kept in anenvironment at 25° C. and 50% RH for 1 hour to form the modificationlayer. An antifouling structure precursor was thus obtained.

Production of Antifouling Structure

A fluorinated oil (KRYTOX GPL103, DuPont Co.) (0.25 mL) was put on thesurface of the antifouling structure precursor dropwise. The oil wasspread by using a cotton and allowed to stand for 5 minutes so that theantifouling structure precursor was impregnated with the oil.Thereafter, excess fluorinated oil was wiped off with a cloth until norainbow pattern was observed. An antifouling structure was thusproduced.

Example 1

Production of Oxide layer

The surface of urethane resin coating was degreased with isopropylalcohol. Thereafter, a solution of perhydropolysilazane (TRESMAIL ANP140-01, Sanwa Kagaku Corp.) was applied onto the surface of the urethaneresin coating by using a cloth impregnated with the solution and thendried. An oxide layer having an uneven surface was thus formed.

An antifouling structure was produced in the same manner as Comparativeexample 1 except that the above-described surface modificationcomposition was applied onto the surface of this oxide layer by flowcoating, and the applied composition was kept in an environment at 25°C. and 70% RH for 1 hour to form the modification layer.

Example 2

An antifouling structure was produced in the same manner as Example 1except that the surface modification composition was used 2 hours afterthe production.

Example 3

An antifouling structure was produced in the same manner as Example 1except that the surface modification composition was used 6 hours afterthe production.

Comparative Example 2

A surface modification composition was produced by mixing 10 mL of themodifier having a perfluoropolyether chain (FLUOROSURF FG-5020TH-0.1,Fluorotechnology, Co.) with 3.9 μL of the first modification acceleratorcontaining 20% of sulfuric acid and 666 μL of the second modificationaccelerator containing 3 ppm of organic platinum catalyst(Pt/1,3-divinyltetramethyldisiloxane complex).

An antifouling structure was produced in the same manner as Comparativeexample 1 except that this surface modification composition was used.

Comparative Example 3

An antifouling structure was produced in the same manner as Comparativeexample 1 except that water was added to the surface modificationcomposition in the amount of 80% of the weight of the modifier having aperfluoropolyether chain.

Comparative Example 4

An antifouling structure was produced in the same manner as Example 1except that the modifier having a perfluoropolyether chain (FLUOROSURFFG-5020TH-0.1) was applied onto the surface of the oxide layer by flowcoating and was kept in an environment at 45° C. and 70% RH for 24 hoursto form the modification layer.

Comparative Example 5

An antifouling structure was produced in the same manner as Example 1except that the modifier having a perfluoropolyether chain (FLUOROSURFFG-5020TH-0.1) was applied onto the surface of the oxide layer by flowcoating and was kept in an environment at 25° C. and 70% RH for 1 hourto form the modification layer.

Comparative Example 6

An antifouling structure was produced in the same manner as Comparativeexample 1 except that the modifier having a perfluoropolyether chain(FLUOROSURF FG-5020TH-0.1) was applied onto the glass surface by using acotton and was kept in an environment at 25° C. and 50% RH for 1 hour toform the modification layer.

Comparative Example 7

Production of Surface Modification Composition

A surface modification composition was produced by mixing 10 mL of themodifier having a perfluoropolyether chain (FLUOROSURF FG-5020TH-0.1)with 2.5 μL of the first modification accelerator containing 20% ofphosphoric acid.

An antifouling structure was obtained in the same manner as Example 1except that this surface modification composition was used.

Comparative Example 8

Production of Surface Modification Composition

A surface modification composition was produced by mixing 10 mL of themodifier having a perfluoropolyether chain (FLUOROSURF FG-5020TH-0.1)with 666 μL of the second modification accelerator containing 3 ppm ofan organic platinum catalyst (Pt/1,3-divinyltetramethyldisiloxanecomplex).

An antifouling structure was obtained in the same manner as Comparativeexample 1 except that this surface modification composition was used.

Comparative Example 9

Production of Surface Modification Composition

A surface modification composition was produced by mixing 10 mL of themodifier having a perfluoropolyether chain (FLUOROSURF FG-5020TH-0.1)with 8.2 μL of the first modification accelerator containing 10% ofacetic acid and 666 μL of the second modification accelerator containing3 ppm of an organic platinum catalyst(Pt/1,3-divinyltetramethyldisiloxane complex).

An antifouling structure was obtained in the same manner as Comparativeexample 1 except that this surface modification composition was used.

Evaluation

The antifouling structure precursors and the antifouling structures ofExamples and Comparative examples were evaluated by the followingmethods. The evaluation results are shown in Table 1.

Coverage Ratio of Thick Area

The surface condition of the antifouling structure precursors wasevaluated as follows. A scanner of an atomic force microscope (AFM) wasvertically moved in the following conditions to obtain a force curve.The cohesion between a probe and a specimen was quantitatively evaluatedfrom the force curve and mapped as described below. The coverage rate ofcovering the oxide layer with the thick area was measured, and it wasconfirmed that the oxide layer is not exposed.

Pretreatment: Each specimen was fixed by the magnetic force of a magnetsheet so that it was electrically grounded.

Device name: NANOSCOPE IIIa (Bruker AXS Co.)+D3100

Probe: Si single crystal probe (OMCL-AC160TS, Olympus Co.)

Measuring conditions: The AFM force curve method (contact mode) with alamp length of 1 μm and a lamp speed of 0.2 Hz was employed. The forcecurve in a 20×20 μm square was measured with a tapping mode AFM, and themaximum cohesion was determined in an attraction force section in areverse scan.

Image processing: A phase image was subjected to (primary) Flattenprocessing. The phase image was further subjected to Gaussian processing(moving average of 500 nm).

Data processing: (Primary) drift correction between forward scan andreverse scan.

Thick area: cohesion of from 3.11 Fmax/nN to below 15.50 Fmax/nN;

Thin area: cohesion of from 0.12 Fmax/nN to below 3.11 Fmax/nN;

Oxide layer-exposed area: cohesion of 15.50 Fmax/nN or more.

AFM phase images of Example 1 to Example 3 and Comparative example 5 areshown in FIG. 3. In FIG. 3, white portions correspond to the thick area.

Measurement of Surface Free Energy

The surface free energy of the antifouling structure precursors wascalculated from the contact angle of a 5 μL ethanol droplet that wasmeasured with an automatic contact meter (DSA 100).

Measurement of Sliding Angle

The sliding angle of a 20 μL pure water on the antifouling structureswas measured with an automatic contact meter (DSA100).

TABLE 1 First modification Second modification Oxide layer acceleratoraccelerator Water Comparative Glass Phosphoric acid Organic Pt Noneexample 1 Example 1 Silazane coating Phosphoric acid Organic Pt NoneExample 2 Silazane coating Phosphoric acid Organic Pt None Example 3Silazane coating Phosphoric acid Organic Pt None Comparative GlassSulfuric acid Organic Pt None example 2 Comparative Glass Phosphoricacid Organic Pt Added example 3 Comparative Silazane coating None NoneNone example 4 Comparative Silazane coating None None None example 5Comparative Glass None None None example 6 Comparative Silazane coatingPhosphoric acid None None example 7 Comparative Glass None Organic PtNone example 8 Comparative Glass Acetic acid Organic Pt None example 9Duration of Surface free Time until Modification Coverage energy Slidinguse conditions rate (mJ/m²) angle Comparative — 25° C. 50% RH, 1 h —12.8 — example 1 Example 1 — 25° C. 70% RH, 1 h 24.7% 13.5 10.7° Example2 2 hours 25° C. 70% RH, 1 h 50.3% 13.5 9°  Example 3 6 hours 25° C. 70%RH, 1 h 85.3% 12.7  9.5 Comparative — 25° C. 50% RH, 1 h — 13.4 —example 2 Comparative — 25° C. 50% RH, 1 h — 13.2 — example 3Comparative — 45° C. 70% RH, 24 h  6.5% 13.14  8.8° example 4Comparative — 25° C. 70% RH, 1 h  3.5% 13.61 — example 5 Comparative —25° C. 50% RH, 1 h — 20.3 — example 6 Comparative — 25° C. 70% RH, 1 h —14.33 15.2° example 7 Comparative — 25° C. 50% RH, 1 h — 15.4 — example8 Comparative — 25° C. 50% RH, 1 h — 16 — example 9

The antifouling structure precursors of Comparative example 1 toComparative example 3 were not able to hold lubricant oil, and a waterdroplet did not slide off. This was because the period of time from theproduction of the surface modification composition to the applicationthereof was short, and an uneven pattern that can hold lubricant oil wasnot formed on the smooth glass surface.

The antifouling structure of Comparative example 4 exhibited sufficientantifouling property since the modification was performed over a longtime. However, since the thick area of the film of the modificationlayer was small, the retention property of lubricant oil was poor.

The antifouling structure of Comparative example 5 had insufficientantifouling property, and dirt was pinned. This was because the surfacemodification composition contained no modification accelerator, and theoxide layer was not completely coated.

The antifouling structure precursor of Comparative example 9 did nothave sufficiently decreased surface free energy since acetic acid wasused as the first modification accelerator.

REFERENCE SIGNS LIST

-   1 Antifouling structure precursor-   2 Oxide layer-   3 Modification Layer-   31 Thick area-   32 Thin area-   4 Lubricant oil-   5 Resin coating-   10 Antifouling structure

1-11. (canceled)
 12. A surface modification method for modifying a surface of an oxide, the method comprising: producing a surface modification composition; and applying the surface modification composition onto a surface of an oxide layer, wherein in producing the surface modification composition, a modifier having a perfluoropolyether chain is mixed with: a first modification accelerator containing an inorganic acid; and a second modification accelerator containing at least one selected from the group consisting of a metal, a metal salt and an organometallic compound.
 13. The surface modification method according to claim 12, wherein the surface modification composition is applied onto the surface of the oxide layer after an elapse of predetermined time from production of the surface modification composition.
 14. The surface modification method according to claim 12, wherein in producing the surface modification composition, the modifier having a perfluoropolyether chain is further mixed with water at the same time.
 15. The surface modification method according to claim 12, further comprising: adding water to the surface modification composition after producing the surface modification composition and before applying the surface modification composition onto the surface of the oxide layer.
 16. A surface modification composition, concurrently comprising: a modifier having a perfluoropolyether chain; a first modification accelerator containing an inorganic acid; and a second modification accelerator containing at least one selected from the group consisting of a metal, a metal salt and an organometallic compound.
 17. The surface modification composition according to claim 16, further comprising water.
 18. A surface modification composition set, comprising: a modifier having a perfluoropolyether chain; a first modification accelerator containing an inorganic acid; and a second modification accelerator containing at least one selected from the group consisting of a metal, a metal salt and an organometallic compound.
 19. An antifouling structure precursor, comprising: a modification layer that contains a modifier having a perfluoropolyether chain; and an oxide layer that has a surface entirely covered with the modification layer, wherein the modification layer is derived from a surface modification composition simultaneously including: a modifier having a perfluoropolyether chain; a first modification accelerator containing an inorganic acid; and a second modification accelerator containing at least one selected from the group consisting of a metal, a metal salt and an organometallic compound, has an uneven film thickness and comprises a comparatively thick area and a comparatively thin area that is dispersed in the comparatively thick area, a coverage rate of covering the oxide layer with the comparatively thick area is equal to or greater than 10%, the comparatively thick area is an area having a cohesion of 3.11 nN or more, and the cohesion is measured by vertically moving a scanner of an atomic force microscope (AFM) on a surface of the antifouling structure precursor to obtain a force curve and quantitatively evaluating cohesion acting between a probe and a specimen from the force curve.
 20. The antifouling structure precursor according to claim 19, wherein the comparatively thick area has the coverage rate within a range from 24.7% to 85.3%.
 21. An antifouling structure, comprising: an antifouling structure precursor, and a lubricant oil on a surface of the antifouling structure precursor, wherein the antifouling structure precursor comprises: a modification layer that contains a modifier having a perfluoropolyether chain; and an oxide layer that has a surface entirely covered with the modification layer, the modification layer is derived from a surface modification composition simultaneously including: a modifier having a perfluoropolyether chain; a first modification accelerator containing an inorganic acid; and a second modification accelerator containing at least one selected from the group consisting of a metal, a metal salt and an organometallic compound, has uneven film thickness and comprises a comparatively thick area and a comparatively thin area dispersed in the comparatively thick area, a coverage rate of covering the oxide layer with the comparatively thick area is equal to or greater than 10%, the comparatively thick area is an area having a cohesion of 3.11 nN or more, and the cohesion is measured by vertically moving a scanner of an atomic force microscope (AFM) on a surface of the antifouling structure precursor to obtain a force curve and quantitatively evaluating cohesion acting between a probe and a specimen from the force curve.
 22. The antifouling structure according to claim 21, wherein the comparatively thick area has the coverage rate within a range from 24.7% to 85.3%. 